High Temperature Effects on CO 2Assimilation Rate in Genotypes of Fragaria Xananassa, F. Chiloensis and F. Virginiana

Abstract

CO ₂assimilation rates (A) in two Fragaria xananassacultivars, ten native F. chiloensisgenotypes, and nine native F. virginianagenotypes were compared in growth chambers held at two day/night temperature regimes: 20/15°C and 30/25°C. Light intensity (PAR) was maintained at 500 μ mol m ^-2s ^-1and day lengths were held at 14 hours. At 20/15°C, F. virginianahad significantly lower A (10.4 μ mol CO ²m ^-2s ^-1) than either F. xananassa(11.6 μ mol CO ₂m ^-2s ^-1) or F. chiloensis(11.7 μ mol CO ₂m ^-2s ^-1). All species showed a significant reduction in A at 30/25°C; however, F. virginianadropped the least at 24%, while F xananassafell 42% and F. chiloensisdropped 54%. ‘Seascape’ and ‘Tribute’ had intermediate levels of A under cool temperatures (12.8 μ mol CO ₂m ^-2s ^-1and 10.4 μ mol CO ₂m ^-2s ¹) and their CO ²assimilation rates were reduced by 39-44% by high temperatures. Several F. chiloensisgenotypes had higher A than the F. xananassagenotypes under cool temperatures, but they were more negatively effected by high temperatures. In F. virginiana,LH 50-4 and RH 18 had A values comparable to ‘Seascape’ and ‘Tribute’, and they showed more modest reduction in A at high temperatures (< 5%). These two genotypes may be good parents to improve heat tolerance in cultivated day-neutral germplasm.